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>Photoactivation of Oxygen-Evolving Enzyme in Dark-Grown Pine Cotyledons: Relationship between Assembly of Photosystem II Proteins and Integration of Manganese and Calcium
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Photoactivation of Oxygen-Evolving Enzyme in Dark-Grown Pine Cotyledons: Relationship between Assembly of Photosystem II Proteins and Integration of Manganese and Calcium
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机译：Photoactivation of Oxygen-Evolving Enzyme in Dark-Grown Pine Cotyledons: Relationship between Assembly of Photosystem II Proteins and Integration of Manganese and Calcium
Dark-grown cotyledons of pine (Pinus thunbergit) did not exhibit O2evolution, but this capability was rapidly activated by illumination for a short period (photoactivation). To examine the biochemical changes which accompany the process of photoactivation in gymnosperms, a method enabling the preparation of highly active O2-evolving photosystem II (PS II) membranes was applied to light-grown, dark-grown, and photoactivated cotyledons. PS II membranes prepared from light-grown cotyledons exhibited high O2-evolving activity, and contained all the intrinsic proteins as well as the three extrinsic proteins (32, 23 and 17 kDa) associated with PS II. These membranes were also found to contain 4.4 Mn and 0.83 Ca/PS II reaction center. PS II membranes from dark-grown cotyledons contained all the intrinsic proteins, but preserved only 32 kDa extrinsic protein, and zero Mn and 0.85 Ca/PS II reaction center. The two extrinsic proteins (23 and 17 kDa) absent in the PS II membranes from dark-grown cotyledons were, however, present as mature forms in whole thylakoid membranes from the corresponding sample. The PS II membranes isolated from photoactivated cotyledons showed a high activity of O2evolution and retained the three extrinsic proteins, 5.3 Mn and 1.1 Ca/PS II reaction center, respectively. The results indicated that Mn and the two extrinsic proteins were tightly integrated in the O2-evolvingapparatus during the process of photoactivation but integration of Ca preceded the integration of Mn by photoactivation.
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